Lunisolar Nutation Research Articles

The Celestial Frame and the Weighting of the Celestial Pole Offsets in the Computation of VLBI-Based Corrections for the Main Lunisolar Nutation Terms.

Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar nutation terms included in the IAU 2006/2000A precession–nutation model. In particular, we pay attention to two factors that affect the estimation of such corrections: the celestial reference frame used in the production of the global VLBI solutions and the stochastic model employed in the least-squares adjustment of the corrections. In both cases, we have found that the choice of these aspects has an effect of a few μas in the estimated corrections.

Polyphony of Short-Term Climatic Variations

It is widely accepted to believe that humanity is mainly responsible for the worldwide temperature growth during the period of instrumental meteorological observations. This paper aims to demonstrate that it is not so simple. Using a wavelet analysis on the example of the time series of the global mean near-surface air temperature created at the American National Climate Data Center (NCDC), some complex structures of inter-annual to multidecadal global mean temperature variations were discovered. The origin of which seems to be better attributable to the Chandler wobble in the Earth’s Pole motion, the Luni-Solar nutation, and the solar activity cycles. Each of these external forces is individually known to climatologists. However, it is demonstrated for the first time that responses of the climate system to these external forces in their integrity form a kind of polyphony superimposed on a general warming trend. Certainly, the general warming trend as such remains to be unconsidered. However, its role is not very essential in the timescale of a few decades. Therefore, it is this polyphony that will determine climate evolution in the nearest future, i.e., during the time most important for humanity currently.

Quantification of corrections for the main lunisolar nutation components and analysis of the free core nutation from VLBI-observed nutation residuals

The attempt to quantify the corrections of lunisolar nutation components was made after analysis of six sets of Earth’s orientation parameters (EOP). The deviations of the long-term nutation components about IAU2006/IAU2000A precession–nutation model are consistent with the uncertainties suggested by Mathews et al. (J Geophys Res Solid Earth, 2002. https://doi.org/10.1029/2001JB000390 ), but they exceed the errors determined in this work. The corrections are validated using the IERS 14C04 and IVS 19q4e combined solutions. After applying the corrections found in this work to the 14C04 nutation residuals, we analyzed the remaining signals, which contain the signature of the free core nutation (FCN). The eigenperiod of the FCN is fixed to the value derived from the resonance of the non-hydrostatic earth model in a priori. The amplitude of FCN is computed by fitting observations to the empirical model using a sliding window, the length of window is determined by taking into account the interference between those close nutation components and the FCN. In addition, we also fitted the nutation residuals by a viscous damping function; both methods produce the same results in the amplitudes of FCN. The magnitude of the free core nutation bears a “V-shape” distribution, and furthermore, the oscillation of the FCN shows a decay and a steady reinforcement before and after 1999. In order to examine the origin of the modulation in FCN’s magnitude, we briefly analyzed the possible damping or beating mechanism behind it. We diagnosed the magnitude and running phase changes of FCN by comparing it with the occurrence of the transient geomagnetic jerks. The weighted root mean square errors of nutation residuals are minimally reduced about $$36\%$$ when the corrections to the 21 nutation components and the FCN signature are considered together.

Nonchaotic and globally synchronized short-term climatic variations and their origin

Careful computations of atmospheric power spectra are done. These computations reveal that these spectra are continuous in the range of timescales from 2 days to 1 year, and so they confirm that weather variations are chaotic; however, the continuity of a part of the atmospheric power spectra, corresponding to the periods from 2 years to one decade is questioned. This part is prominent by the existence of several narrow bands of increased spectral density centered at the subharmonics 2:1, 3:1, and 4:1 of the Chandler wobble in the Earth’s pole motion (~ 1.2 years); the superharmonics 1:2, 1:3, and 1:4 of the Luni-Solar nutation of the Earth’s rotation axis (~ 18.6 years) as well as the superharmonics 1:2, 1:3, and 1:4 of the 11-year cycle of the Sun spots. The existence of similar bands in the El Nino–Southern Oscillation (ENSO) power spectra was recognized many years ago; however, it turns out that the above spectral bands also are seen in spectra of the atmospheric characteristics outside of tropics. Moreover, the respective climatic variations are globally synchronized. The synchronization takes place because the above-mentioned external periodicities must influence short-term climatic variations everywhere on the Earth. It is very probable that the periods of the external periodicities indicated are incommensurable with each other. Therefore, if these periodicities actually influence short-term climatic variations, they would have to do it discordantly. As a result, no resonances can exist which could make the affected climatic variations to be chaotic. A linear dependence of logarithms of serial numbers of the spectral bands on logarithms of the band magnitudes as well as a linear decrease of the accumulated sum of the squared autocorrelations of the respective atmospheric characteristics confirm that the dynamics of the interannual to decadal climatic variations are not chaotic.

Corrections and new developments in rigid earth nutation theory

We present here the new tables REN-2000 of the nutation for a rigid Earth model, starting from Hamiltonian theory, with a level of truncature at 0.1 mu as for individual coefficients instead of 5 mu as (Kinoshita & Souchay 1990). For this presentation to be achieved we first carry out the calculations of the second-order effects due to crossed-nutations and spin-orbit coupling, at the same level of truncation as above. This paper is the third and last one in the frame of the complete reconstruction of the theory of the rigid Earth nutation. It is the complementary part to previous studies concerning the luni-solar nutation involving indirect planetary effects (Souchay & Kinoshita 1996), and the influence of the second-order geopotential (J(3), J(4)) and of the direct planetary effect (Souchay & Kinoshita 1997). Quasi-diurnal and sub-diurnal nutations coming from the harmonics of degree 2, 3 and 4 of the geopotential are also included in REN-2000, their values being taken from Folgueira et al. (1998a,b). A presentation of the series REN-2000 is done at the end of the paper, with separated informations for each contribution.

Dynamics of an Artificial Satellite in an Earth-Fixed Reference Frame: Effects of Polar Motions

AbstractIn an Earth-fixed reference frame, polar motions (precession, lunisolar nutation, free nutation) introduce small apparent forces in the equations of motion of an Earth satellite. We discuss the possibilities (a) of integrating the orbit in an Earth-fixed frame when tracking data are used for geophysical applications, and (b) of determining from orbital data a set of unknown parameters describing the long-period wandering of the pole.